Compositions and methods relating to functionalized sands

ABSTRACT

Described herein are compositions and methods relating to functionalized sands or soils.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a U.S. National Stage of InternationalApplication No. PCT/IB2017/056157, filed Oct. 5, 2017, which claimspriority to U.S. Provisional Patent Application Ser. No. 62/550,264,filed Aug. 25, 2017 and U.S. Provisional Patent Application Ser. No.62/404,958, filed Oct. 6, 2016, the entire disclosures of which are bothhereby incorporated by reference.

TECHNICAL FIELD

The present disclosure generally relates to compositions and methods tofunctionalize sands or soils, and in an aspect compositions and methodsrelating to hydrophobic sands or soils as described herein.

BACKGROUND

Desert areas pose a number of challenges in regards to water and storms.For example sufficient sources for useable water, in particulardesalinated water, and its use for agriculture, is a challenge. Storms,in particular dust and sand storms pose a further challenge.

Two of the biggest environmental and economic challenges for desertagriculture are: (1) large consumption of water due to intenseevaporation and imbibition in the soil, and (2) deposition of commonsalts, e.g. NaCl, in the top soil from partially salty irrigation water(also known as sodication of soil). One way to meet these challenges isthrough surface modifications of sand or soil in and around agriculturalsystems that can “functionalize” sand or soil. These modifications, suchas improving the hydrophobicity of inherently hydrophilic sand or soil,allow improved water retention and decreased salt deposition byemploying functionalized sand or soil into agricultural systems.Functionalized sand or soil also can be used in desalination processesto produce water suitable for use in agriculture and to reduce theseverity of dust or sand storms.

Current technologies exist for functionalizing and modifying the surfaceproperties of sand. These technologies, such as the use of organosilanesto improve hydrophobicity, are very costly. They also suffer otherdrawbacks from an ease-of-use perspective. These issues prevent thewidespread adoption and implementation of functionalized sand intodesert agricultural systems. Accordingly, there is a need to address theaforementioned deficiencies and inadequacies and to address theaforementioned challenges.

SUMMARY

Provided herein are methods for making a functionalized sand or soil anda functionalized sand or soil composition and also methods of use of thefunctionalized sand or soil composition. The composition can, interalia, be for use in agricultural systems, including desert agriculturalsystems, in producing desalinated water via membrane distillation, andin reducing the severity of dust and sand storms.

Described herein, in an embodiment, is a method of making a modifiedsand or soil. As used herein, sand can mean “soil” and vice versa, orboth. The method can result in making a functionalized sand, afunctionalized soil, or a composition comprising both a functionalizedsand and a functionalized soil. The method of making the modified sandand/or soil can comprise: providing an unmodified sand or soil or both;dissolving a modifying agent, such as wax, into a solvent to create amodification mixture, such as a wax solution; mixing the unmodified sandand/or soil with modification mixture; incubating the unmodified sandand/or soil and modification mixture for a length of time, at atemperature or varying temperature, and at a pressure or a varyingpressure to create the modified sand and/or soil. In any one or moreaspects, the method can further include evaporating the solvent;condensing the evaporated solvent to re-create a liquid solvent; andstoring the liquid solvent in a storage vessel. As used herein, whenreference is made to “sand or soil” it should be understand that thiscan also include a combination of both sand and soil.

In an embodiment, the method of producing superhydrophobicity in sand orsoil can comprise the steps of: a) obtaining a sand or soil composition;b) washing the sand or soil composition; c) drying the sand or soilcomposition; d) obtaining a wax; e) dissolving the wax into a solvent toform a wax solution; e) adding the sand or soil composition to acontainer; f) adding the wax solution to the container; g) mixing thewax solution and the sand or soil composition within the container at afirst pressure (P1) and at a first temperature (T1) for a first periodof time (t1); h) bringing the mixture up to but under a boil, oralternatively up to a slow boil, over another time period (t3); and i)subsequently maintaining the mixture at a constant pressure for a finaltime period (t4) to form said superhydrophobic sand or soil includingthe sand or soil composition coated with wax.

In an embodiment, the method can further include the steps of: reducingthe first pressure (P1) in the container to a second pressure (P2) thatis lower than the first pressure (P1) over a second time period (t2),the second time period (t2) being less than that of the first timeperiod (t1); reducing the second pressure (P2) in the container at aconstant rate over the third period of time (t3) to a third pressure(P3), the third period of time (t3) being longer than the second periodof time (t2) and the third pressure (P3) being lower than the secondpressure (P2); once reaching the third pressure (P3) maintaining thepressure in the container at the third pressure (P3) for the fourth andfinal period of time (t4); and normalizing the pressure in the containerfrom the third pressure (P3) up to atmospheric pressure to form saidsuperhydrophobic sand or soil including the sand or soil compositioncoated with wax.

In any one or more aspects of the method, the sand or soil compositioncan comprise a plurality of particles comprising one or more of SiO₂,CaCO₃, Al₂O₃, Fe₂O₃, TiO₂, P₂O₅, K₂O, CaO, MgO, Na₂O, and/or MnO₂ andwherein each of the particles has a maximum dimension of less than about600 μm. The method can further include filtering the sand or soilparticles after drying the sand and adding the filtered sand or soilparticles to the container, wherein the filtering isolates sand or soilparticles having a longest dimension of about 600 μm or less. The dryingcan be performed with a thermal convection oven, using sunlight, orusing natural wind convection, individually or in combination. The stepof obtaining the wax can include preparing the wax by grating or shavingthe wax, individually or in combination, and using about 1 mL of solventto 2 g of particles. The container can be a rotary evaporator and thecontainer is able to support a reduced pressure reduced to about 10 mbarand optionally contains one or more baffles to aid in the mixing of thewax solution and the sand composition within the container. The waxsolution and sand or soil composition can be present in the container ina proportion of about 1:200 to about 1:200 grams of wax to grams of sandor more than 1:200 grams of wax to grams of soil. The mixing can beperformed by the rotary evaporator rotating at a rate of about 10 toabout 150 rpm. The first temperature (T1) can be about 40° C. to about55° C., and below the melting point of the wax. The first pressure (P1)can be about 1000 mbar, or one atmosphere, of pressure. The first periodof time (t1) can be about 1 minute to about 5 minutes. The firsttemperature (T1) can be about 40° C. and wherein during the step ofreducing the second pressure (P2) to the lower pressure (P3) thetemperature can be raised from said first temperature (T1) to a secondtemperature (T2) of about 55° C. The second pressure (P2) can be about100 mbars to about 900 mbars. The third pressure (P3) can be about 10mbars to about 500 mbars. The second period of time (t2) can be up toabout 2 minutes. The third period of time (t3) can be about 5 to about25 minutes. The fourth time period (t4) can be about 1 to about 5minutes. The third period of time (t3) can be selected to be slow enoughto prevent boiling or rapid boiling of the wax solution in thecontainer. The third period of time (t3) and the third pressure (P3) canbe selected to bring the mixture to a boil (to slow boil or up to a boilwithout actually boiling). The solvent can be selected from the groupconsisting of diethyl ether, pentane, dichloromethane, and combinationsthereof. The solvent can be selected from the group consisting ofmethyl-t-butyl ether (MBTE), petroleum ether (ligroin), chloroform,tetrahydrofuran (THF), hexane, cyclohexane, triethyl amine, gasoline,toluene, and mixtures thereof.

In any one or more aspects, the methods described herein can use beachsand, desert sand, or any other source of sand or soil with smallerparticle sizes such as silt or clay. The modifying agents as used hereincan be comprised of wax. The wax can be common wax, paraffin wax, soywax, palm wax, or bees wax, among others, individually or incombination.

In various embodiments, a functionalized sand and/or soil composition isalso described herein. The composition can be a surface modified sand orsoil, modified to change the surface to a superhydrophobic surface. Themodifying agent can be a wax as described further herein. Thefunctionalized sand and/or soil composition can be a composition made byany one or more of the methods described herein.

In an embodiment, the modified composition of sand or soil can includeone or more particles of sand or soil. The one or more particles of sandor soil can have a size, and the surface of the particles can be coatedwith a functionalizing agent such as a hydrophobic layer. Thecomposition of sand or soil with particles having a hydrophobic layercan have a liquid roll off angle of about 3 to 7 degrees, about 4 to 6degrees, or about 5 degrees, for a layer of modified sand or for one ormore particles themselves. The curvature of the liquid meniscus at thesolid-vapor interface can have a contact angle, θ₀<90°.

In any one or more aspects, the size of the one or more particles can beabout 75 μm to about 150 μm, and the one of more particles can becomprised of SiO₂, CaCO₃, Al₂O₃, Fe₂O₃, TiO₂, P₂O₅, K₂O, Cao, MgO, Na₂O,or MnO₂. The sand or soil particles to be modified can be desert sand orbeach sand, or any other type of sand or soils with smaller particlesizes such as silt or clay. The sand or soil can be modified to includea hydrophobic layer that can coat the surface of one or more of theparticles. The hydrophobic layer can be a wax layer. The wax layer canbe a layer of common wax, paraffin wax, palm wax, bees wax, and soy wax,individually or in combination. In one or more aspects, the modifiedcomposition of sand or soil can comprise a hydrophobic or asuperhydrophobic sand or soil mulch including the modified sand or soilparticles. The ratio of wax to sand or soil an be in the range of 1:200to 1:2000 grams of wax to grams of sand, or more than 1:200 grams of waxto grams of silt or clay soils, providing a thin hydrophobic layer ofwax consistently over the surface of the particles. In various aspectsthe thickness of the wax on the particles can be about 100 nm or less,about 80 nm or less, about 60 nm or less, about 40 nm or less, about 35nm or less, about 30 nm or less, or about 20 nm or less. The thicknessof the wax on the sand or soil particles can be in the range of about 10nm to about 100 nm or anywhere in between, for example, about 10 nm toabout 80 nm, about 10 nm to about 60 nm, about 10 nm to about 40 nm,about 15 nm to about 35 nm, or about 20 nm to about 30 nm, preferablyabout 20 nm.

Also described herein are methods for reducing irrigation requirementsfor an agricultural system. In one or more aspects, the methods caninclude providing a layer of the aforementioned mulch on top ofagricultural top soil. In an aspect, the thickness of the mulch canrange from 2 mm to about 20 mm, for example about 3-5 mm, on top of thesoil. In an embodiment, the methods can comprise: tilling soil within anagricultural system, wherein the tilled soil has one or more apexes andone or more troughs, wherein a difference in height exists between theone or more apexes and the one or more troughs; planting one or moreseeds in the one or more troughs of the tilled soil; and distributingthe aforementioned modified sand in any one or more of its aspects onthe one or more apexes of the tilled soil. The method can furtherinclude irrigating the tilled soil.

Also described herein are methods of reducing fertilizer leaching. In anembodiment the method of reducing fertilizer leaching can comprise:distributing a layer of modified sand or soil according to any one ormore aspects of the present disclosure throughout an agriculturalsystem; distributing a layer of soil on top of the layer of modifiedsand, soil, and/or the mulch; distributing fertilizer throughout thelayer of soil; and planting seeds in the layer of soil. The method canfurther include irrigating the soil.

Further described herein is a method of reducing evaporation in a field.In an embodiment, the method of reducing evaporation in a field cancomprise: providing a layer of soil; planting seeds in the layer ofsoil; irrigating the layer of soil; and distributing modified sand,soil, and/or the mulch according to the present disclosure on top of thesoil.

Also described herein is a method of resisting forces generated by oneor more flows of fluid. In an embodiment the method can comprise: makinga modified sand according to any one or more of the aspects of thepresent disclosure; providing the modified sand or soil; and placing themodified sand on a surface subject to forces generated by one or moreflows of fluid.

Also described herein is a fluid filter. In an embodiment, the fluidfilter can comprise a modified sand or soil containing modified sand orsoil particles according to any one or more of the aspects of thepresent disclosure; a container with pores configured to receive andhold the modified sand or soil, wherein the pores have a cross-sectionalarea smaller than a maximal average cross-sectional area of the modifiedsand or soil particles; wherein the container is configured to receive afluid with a concentration of ions and/or particulate matter; andwherein the container is configured to pass the fluid through themodified sand or soil and discharge the fluid from the filter. In one ormore aspects, the fluid filter can be used as the membrane in a membranedistillation process as further described below.

Also described herein is a method of resisting fluid percolation andwater loss in soils. In an embodiment, the method can comprise: having amodified sand or soil made according to any one or more of the aspectsof the present disclosure; providing the modified sand or soil; andplacing the modified sand or soil under a layer of 10 cm to 2 μm ofsoil.

Also described herein is a method of resisting corrosion and preservingmaterials. In an embodiment, the method can comprise: having a modifiedsand or soil made according to any one or more of the aspects of thepresent disclosure; providing the modified sand or soil; and placing themodified sand or soil around the objects to be protected againstcorrosion.

Also described herein is a method of thermally insulating structures. Inan embodiment, the method can comprise: having a modified sand or soilmade according to any one or more of the aspects of the presentdisclosure; providing the modified sand or soil; and placing themodified sand or soil around the objects to be insulated against thermalloss of gain.

Other systems, methods, features, and advantages of the presentdisclosure for systems and methods for compositions and methods relatingto inexpensive functionalized sands or soils, will be or become apparentto one with skill in the art upon examination of the following drawingsand detailed description. It is intended that all such additionalsystems, methods, features, and advantages be included within thisdescription, be within the scope of the present disclosure, and beprotected by the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the disclosure can be better understood with referenceto the following drawings. The components in the drawings are notnecessarily to scale, emphasis instead being placed upon clearlyillustrating the principles of the present disclosure. Moreover, in thedrawings, like reference numerals designate corresponding partsthroughout the several views.

FIG. 1A depicts a photograph of hydrophobic sand with water wherein thewater is not able to penetrate the sand.

FIG. 1B are high-speed micrographs of a water drop (2 μL) impinging on apacked bed of hydrophobic sand from a height of 2 cm.

FIG. 2 depicts how water imbibes in granular sand media and itsinherently hydrophilicity. Since sand comprises primarily of silica andcalcite, the contact angle of water θ₀<90°. Thus, as water comes in tocontact with, approximately spherical, sand particles the mechanicalequilibrium between interfacial tensions leads to a concave liquidmeniscus. This curvature creates a capillary pressure, also known as theLaplace pressure, that drives water inward. An approximate magnitude ofthis pressure can be estimated by considering sand particles to beapproximately spherical with diameters 75 μm<d<150 μm and spacing,P_(L)=2γ_(LV)×cos θ₀/r₂≈6-600 kPa, where γ_(LV)=73 mN/m is the surfacetension of the air-water interface and r₂=20 μm to 200 nm is a possiblerange for the radio of curvature due to multiscale roughness of grains.

FIG. 3A depicts how water imbibition will be prevented insurface-modified hydrophobic granular (sand or soil) media. Typicalcontact angle of water on wax is, θ₀≈105°. Thus, the air-water interfacein contact with sand or soil particles will form a convex meniscus dueto the mechanical equilibrium of interfacial tensions. This curvaturecreates a Laplace pressure that prevents imbibition of water intosuperhydrophobic sand or soil.

FIG. 3B illustrates a schematic for surface modification of sand or soilby treating it with a solution of wax dissolved in toluene, impartinghydrophobicity to the sand or soil. Subsequently, toluene is allowed toevaporate and condensed, leaving behind wax coated hydrophobic sand orsoil.

FIGS. 4A and 4B are environmental scanning electron micrographs of wateron ordinary sand (FIG. 4A) vs superhydrophobic sand granules of thepresent disclosure (FIG. 4B). To condense water droplets in an electronmicroscope, partial pressure of water vapor is increased and temperatureis dropped. (A) Water droplets on ordinary sand granules (θ_(r)≈30°) and(B) water droplets on a superhydrophobic sand granule, (θ_(r)≈90°).These images show that the contact angles are greater on wax-coated sandthan on uncoated sand.

FIG. 4C depicts a sessile water droplet on a packed bed of hydrophobicsand. The roll-off angle was found to be, θ_(roll-off)≈5°. The apparentcontact angle is θ_(A)≈150° and this droplet can sit on top of the sanduntil its complete evaporation.

FIG. 5 is photograph of an embodiment of the present superhydrophobicsand holding a 60-cm column of water, with rhodamine dye. Thisexperiment continued for over 1 week during which, water could notpenetrate into the superhydrophobic sand.

FIG. 6 illustrates the results of a mixed sand wetting experiment.Superhydrophobic sand according to embodiments of the present disclosurewas mixed with normal (hydrophilic) sand at different fraction and thecontact angle that a droplet made with a packed bed of the sand mixturewas measured. This graph shows that even to a mixture down to 10% ofhydrophobic sand, the superhydrophobicity can be seen. To fractionsbelow 10%, the droplet was very unstable and would wet the sand bedunder small disturbances.

FIGS. 7A and 7B show results from an ambient-condition evaporation studyperformed at KAUST, Thuwal, Saudi Arabia. FIG. 7A is a picture of thepots used for ambient-condition evaporation experiment. All the potshave the same amount of soil (75 g) and the same initial amount of water(132 g). Positioning the pots in (x,y) matrix, the pots at the bottomleft [(1,1),(1,2)] have a layer of wax-coated beach sand, [(1,3), (1,4),(1,5), (2,1)] have a top layer of hydrophobic sand mixed with soil,[(2,2), (2,3)] have a hydrophobic layer (outer ring) and a normal sandlayer (central circle), [(2,4), (2,5), (3,y), (4,1), (4,2), (4,3)] havea normal sand layer on top, [(4,4), (4,5), (5,y), (6,1), (6,2), (6,3)]have a hydrophobic sand layer and [(6,4), (6,5)] have no sand layer.Pots in the same category have different thicknesses of the hydrophobicsand layer acting as a mulch. FIG. 7B illustrates experimental resultsto compare the evaporative losses from common soil (soils that are nottreated with wax, in this example the soil layer beneath thesuperhydrophobic sand) saturated with water using different thicknessesof layers of normal sand, hydrophobic sand and bare soil. Temperaturesranged from 26 to 48° C. and relative humidity from 14 to 93% with anaverage of 48%. The initial time corresponds to 9:45 a.m. on Oct. 10,2016. The study compares evaporation loss from common soil saturatedwith water using different thicknesses of the layers of normal sand,hydrophobic sand and bare soil.

FIG. 8 is a graphic illustrating schematics of water loss from bare soil(left) compared to soil covered with the present superhydrophobic sandor soil (right). The evaporation loss is significantly reduced with thehydrophobic sand or soil cover. The infiltration loss can also becontrolled with frequent and low volume irrigation. However, if thistype of irrigation is applied in bare soil, the loss through evaporationwill increase considerably. Overall, the hydrophobic sand or soil coverincreases the amount of water available for plants to use for theirmetabolism and for transpiration.

FIG. 9 shows field design for tomato and barley plants. The image showsthe plot distribution (superhydrophobic sand versus bare soil) on thefield, as well as the sensor locations.

FIG. 10A is a photograph showing tomato plots. The image shows the plotdistribution (hydrophobic sand layer versus bare soil) on the field forthe fresh water study.

FIG. 10B shows barley plots. The image shows the barley plots undersaline irrigation study.

FIG. 11A depicts humidity sensor data from the tomato field experiments.Sensor data from the Hada Al sham field. This sensor data was fromsensors 10 cm below the surface in fresh water conditions, and a datapoint was collected every 5 minutes. The data is for a two-month period.

FIG. 11B depicts humidity sensor data from the barley field experiments.Sensor data from the Hada Al sham field. This sensor data was fromsensors 10 cm below the surface in fresh water conditions, and a datapoint was collected every 5 minutes. The data is for a four-monthperiod.

FIGS. 12A and 12B are boxplots of phenotypic data for field-grown barley(FIG. 12A) and tomato (FIG. 12B) plants under freshwater and salineirrigation (blue, left half, and orange, right half, background,respectively), with or without a superhydrophobic sand mulch layer onthe soil surface (white and beige or darker boxplots, respectively).Each boxplot represents the distribution of measurements of differenttraits taken for individual plants from 3 replicate plots for eachtreatment group. Treatment groups were assigned letters based on aone-way ANOVA with post hoc Tukey's test (p<0.05), with differentletters designating groups that are significantly different. FM, freshmass.

FIG. 13 is a picture of liquid marbles. The photograph of two liquidmarbles was made by rolling a droplet of water on top of an embodimentof the present hydrophobic sand. The formation of the liquid marbles canbe observed when the hydrophobic sand particles adhere to the surface ofthe water droplet making a (roughly) monolayer of particles.

FIG. 14 shows photographs from the liquid marbles evaporationexperiment. A visual comparison of evaporation rates of water dropletsagainst liquid marbles. On the left droplet and marble with initialvolume of 10 μL and on the right, marble and droplet with initial volumeof 80 μL at two different time points.

FIG. 15 visualizes data from the liquid marbles evaporation experiment.This experiment shows the properties of the liquid (water) marbles madewith an embodiment of hydrophobic sand as described herein in reducingthe evaporation rates when compared with water droplets.

FIGS. 16A-16B are photographs showing cone angle of normal (FIG. 16A)versus superhydrophobic sand (FIG. 16B). The wax coating increases thecoefficient of friction (tangent of half, of 180 degrees minus the coneangle). So, the lower the cone angle, the greater the coefficient offriction between the sand particles.

FIGS. 17A and 17B illustrate a dust lifting experiment and datatherefrom. FIG. 17A shows an experimental setup where a fan was placedat a distance from a petri dish containing sand. FIG. 17B shows resultsfor the experiment comparing normal sand, hydrophobic sand andhydrophobic sand baked (after being exposed to 50° C. for 24 h). It canbe noted that the mass of sand lost due to the wind is greater for thenormal sand when compared to the hydrophobic sands. The wind velocitywas qualitatively measure based on the distance between the blower andthe petri dish containing sand.

FIG. 18A is a schematic of membrane distillation using an embodiment ofa wax-coated hydrophobic sand according to the present disclosure.

FIG. 18B is a schematic of the vapor flow from a warmer salty water to acooler desalinized region.

FIG. 19 depicts a 48-hour long study comparing losses of water throughordinary farm soil (squares), ordinary farm soil covered with a 2-3 mmthick ordinary sand layer (triangles), and ordinary farm soil coveredwith a 2-3 mm thick hydrophobic sand layer (circles).

FIG. 20 illustrates a schematic of a hydrophobic sand layer acting as amulch layer on a freshly tilled field with regularly spaced seeds.

FIG. 21 is a flowchart depicting an embodiment of a method of makingfunctionalized sand and/or soil as described herein.

FIG. 22 is a flowchart depicting another embodiment of a method ofmaking functionalized sand and/or soil as described herein.

DETAILED DESCRIPTION

Described below are various embodiments of compositions and methodsrelating to functionalized sands or soils, including hydrophobic sandsor soils, and their uses according to the present disclosure. Althoughparticular embodiments are described, those embodiments are mereexemplary implementations of the system and method. One skilled in theart will recognize other embodiments are possible. All such embodimentsare intended to fall within the scope of this disclosure. Moreover, allreferences cited herein are intended to be and are hereby incorporatedby reference into this disclosure as if fully set forth herein. Whilethe disclosure will now be described in reference to the above drawings,there is no intent to limit it to the embodiment or embodimentsdisclosed herein. On the contrary, the intent is to cover allalternatives, modifications and equivalents included within the spiritand scope of the disclosure.

Discussion

Before the present disclosure is described in greater detail, it is tobe understood that this disclosure is not limited to particularembodiments described, as such may, of course, vary. It is also to beunderstood that the terminology used herein is for the purpose ofdescribing particular embodiments only, and is not intended to belimiting, since the scope of the present disclosure will be limited onlyby the appended claims.

Where a range of values is provided, it is understood that eachintervening value, to the tenth of the unit of the lower limit (unlessthe context clearly dictates otherwise), between the upper and lowerlimit of that range, and any other stated or intervening value in thatstated range, is encompassed within the disclosure. The upper and lowerlimits of these smaller ranges may independently be included in thesmaller ranges and are also encompassed within the disclosure, subjectto any specifically excluded limit in the stated range. Where the statedrange includes one or both of the limits, ranges excluding either orboth of those included limits are also included in the disclosure.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this disclosure belongs. Although any methods andmaterials similar or equivalent to those described herein can also beused in the practice or testing of the present disclosure, the preferredmethods and materials are now described.

All publications and patents cited in this specification are hereinincorporated by reference as if each individual publication or patentwere specifically and individually indicated to be incorporated byreference and are incorporated herein by reference to disclose anddescribe the methods and/or materials in connection with which thepublications are cited. The citation of any publication is for itsdisclosure prior to the filing date and should not be construed as anadmission that the present disclosure is not entitled to antedate suchpublication by virtue of prior disclosure. Further, the dates ofpublication provided could be different from the actual publicationdates that may need to be independently confirmed.

As will be apparent to those of skill in the art upon reading thisdisclosure, each of the individual embodiments described and illustratedherein has discrete components and features which may be readilyseparated from or combined with the features of any of the other severalembodiments without departing from the scope or spirit of the presentdisclosure. Any recited method can be carried out in the order of eventsrecited or in any other order that is logically possible.

Embodiments of the present disclosure will employ, unless otherwiseindicated, techniques of sample preparation, water analysis, waterfiltration, mathematical modeling, and the like, which are within theskill of the art. Such techniques are explained fully in the literature.

It is to be understood that, unless otherwise indicated, the presentdisclosure is not limited to particular methods of functionalizing sandsor soils and functionalized sand or soil compositions or functionalizedsoils with smaller particle sizes, in particular methods andcompositions for hydrophobic sands, or the like, and their uses as suchcan vary. It is also to be understood that the terminology used hereinis for purposes of describing particular embodiments only, and is notintended to be limiting. It is also possible in the present disclosurethat steps can be executed in different sequence where this is logicallypossible.

It must be noted that, as used in the specification and the appendedclaims, the singular forms “a,” “an,” and “the” include plural referentsunless the context clearly dictates otherwise. Thus, for example,reference to “a support” includes a plurality of supports. In thisspecification and in the claims that follow, reference will be made to anumber of terms that shall be defined to have the following meaningsunless a contrary intention is apparent.

Definitions

“Common soil” or “common soils” as used herein refers to sands or soilsthat are not treated with wax.

“Rapid boil” or “rapid boiling” as used herein refers to a boil that isperformed under higher difference of actual pressure and vapor pressure,provoking a more vigorous bubbling of the liquid, solvent, aqueoussolution, aqueous suspension, and the like.

“Slow boil” or “slow boiling” as used herein refers to a boil that isdone when the actual pressure is closer to the vapor pressure, provokinga gentler (less vigorous) bubbling.

Description

The present disclosure is directed to compositions and methods relatingto functionalized sands and/or soils and functionalized sand and/or soilcompositions, for example hydrophobic sands, and their uses such as in,inter alia, agriculture, producing desalinated water via membranedistillation, and reducing dust and sand storms. In an aspect, thefunctionalized soils can have smaller particle sizes than thefunctionalized sands. As used herein, sand can mean “soil” and viceversa, or both.

Previous work has attempted to make hydrophobic sands with waxes, suchas: U.S. Pat. No. 7,160,379¹, CN103306260 B², CN1104390 C³, U.S. Pat.No. 6,235,070B1⁴, among others. Some require melting of wax followed bymixing with sand. Methods as described in U.S. Pat. No. 7,160,379¹despite its high thermal and mechanical requirements, do not provide auniform coating of wax over sand grains; lack of a uniform coating lendsthe functionalized sand unable to resist water for long periods of time,and the hydrophobicity of the sand tends to fail starting at 60 minutes.

The processes in the literature above which utilize the melted wax tocoat sand either require a very high quantity of wax, leading todiminishing returns based on cost, or produce bad quality coatingbecause the wax does not form a uniformly distributed layer on thesurface of the sand grains, which is the case for the cited patent U.S.Pat. No. 7,160,379¹ and also for the other references¹⁻¹¹ that rely onthe same methodology of melting wax and mixing with sand to hydrophobizeit.

It is worth mentioning that the present process for making sandhydrophobic only uses 1 g of wax per 200 g of sand, or even less, ofsand (good results were obtained even when 1 g of wax per 2000 g of sandwas used). The process cited in U.S. Pat. No. 7,160,379¹ claims to usefrom 0.01 to 10% (weight ratio of wax blend to total coated sandweight). However, the present process was able to effectively use 0.050%wax (1 g of wax per 2000 g of sand) for beach sand particles sieved forsizes <600 μm, and yet truly make hydrophobic sand. Thus, the presentprocess uses much less wax and is able to make a hydrophobic sandcomposition that can serve as a much with a more homogeneous coating.

Chinese patent CN103304173 B¹² creates a solution of wax and toluenewhich is then mixed with common sand in a rotary evaporator. The tolueneis evaporated and recovered, but the amount of wax required makes thedisclosed method financially impractical due to the cost of materialsand the quality of coating provided.

Other researchers have exploited paraffin wax by heating it up to 80degrees and adding sand to it. (CN 103290832). This process is miredwith difficulties, such as (i) high energy consumption due to arequirement that high temperature be used to melt the wax, (ii) dealingwith high-viscosity wax, (iii) thick wax coatings on sand, which mightincrease overall costs and processing time, and (iv) lack of homogenouscoating of the sand surface with the wax. The dynamic viscosity ofparaffin wax can vary by a factor in the range 7-3 mPa-s as thetemperature changes from 60-100° C. This means that a precise control oftemperature is critical in the reference mentioned above to avoid thepotential of jamming the mixing impellers or pipes/columns.

A strategy to coat polystyrene (PS) on sand by dissolving PS in toluenehas also been reported. (CN 103283577). It, too, has challenges. Forexample, it requires use of high temperature and pressure to separatethe toluene solvent from the solute mixture. It also requires arelatively large amount of the PS to coat the sand, for example 10 g ofPS to 30 kg of as compared to the present disclosure. Accordingly, thereexists a need in the art for improvements relating to functionalizedsand or soil.

In various aspects, described herein is a surface modification to sandor soil for the functionalization of the sand or soil. As describedherein, the sand can be common sand, or common soils with smallerparticle sizes, and can comprise a mixture of particles made of variousminerals. Sand as described herein can be sand that is found on beachesor in deserts, or in soils with low organic matter content. Sandcompositions can be volcanic in origin. Minerals that can form particlesof common sand or common soils (silt and clay) or other sandcompositions can include quartz (SiO₂), aragonite (CaCO₃), alumina(Al₂O₃), iron oxide (Fe₂O₃), and titania (TiO₂). As used herein, sandcan refer to common sand or silt or clay soils, other compositions ofsand or soil, particles of sand or soil, grains of sand or soil, or acomposition with particles and/or grains of sand or soil.

In various aspects, the sand or soil can be 0.75-600 micron sizedparticles and anywhere there between, such as silica beads (hollow orsolid), or silt. Particles of sand as described herein can be sized inlength from about 0.75 μM to about 150 μM. Particles of sand or soil asdescribed herein can have a diameter of about 600 μM or less, 500 μM orless, 400 μM or less, 300 μM or less, 200 μM or less, for example in therange of 75 μM to about 150 μM. As used herein, particle size can referto a length, a diameter, a radius, a circumference, a width, a height,or other physical dimension. Sand or soil particles can be approximatelyspherical and can have an average distance from one sand or soilparticle to another in a composition of sand or soil. Sand or soilcompositions and particles can be inherently hydrophilic with a contactangle of water θ₀<90° without any modifications to the particles within.

In various aspects, described herein are sand or soil compositions thathave sand grains or soil particles with modified surfaces andhydrophobic properties to functionalize the sand or soil. Particles ofsand or soil as described herein can be functionalized or modified toalter their surface properties. Surface properties of sand or soilparticles can be modified with a surface modification agent to createmodified or functionalized sand or soil. Sand or soil compositions asdescribed herein can have modified surface properties that render thesurface of the sand or soil more hydrophobic. Sand or soil compositionsas described herein can have modified surface properties that raisetheir coefficient of friction. Sand or soil compositions with a modifiedsurface as described herein can have a higher coefficient of frictionthan unmodified sand or soil that imparts resistance to forces of fluidflow. Sand or soil compositions with a modified surface as describedherein can have a higher Laplace pressure generated by the particles ofthe composition. Sand or soil compositions with a modified surface asdescribed herein can have a higher Laplace pressure and impede the flowof a fluid. Sand or soil compositions with a modified surface asdescribed herein can have a higher Laplace pressure and impede the flowof liquid water, while permitting the flow of water vapor betweenparticles.

In various aspects, the sand or soil can be a hydrophobic sand or soilthat is modified to alter the way the sand or soil particles interactwith water. A hydrophobic substance can be applied to the surface of thesand or soil particles. Sand or soil particles can be coated with ahydrophobic substance to modify their surface properties so that theparticles repel water in order to create a hydrophobic sand or soil.Sand or soil particles can be coated with a hydrophobic substance tomodify their surface properties so that a composition of modified sandor soil has a higher Laplace pressure generated by the particlestherein. The surface of sand or soil particles in a modified orhydrophobic sand can be modified so that they have a contact angle θ₀with water of greater than 90°, θ₀>90°, for example >95°, >100°, >105°,or >110°. The coating of the particles can be a thin coating. In one ormore aspects, the coating of the hydrophobic substance can have athickness of approximately 100 nm of the wax or less, for example 50 nm,40 nm, 30 nm, 20 nm or less. In one or more aspects, a hydrophobicand/or superhydrophobic sand or soil mulch can be formed or comprised ofthe modified sand or soil.

In various aspects, described herein is a method of imparting a surfacemodification onto particles of sand or soil. Modified or hydrophobicsand or soil can be modified with a hydrophobic substance, In any one ormore aspects, the hydrophobic substance sand or soil particles can becoated with a wax in a thin layer to modify the sand or soil, such asthat described above. In an embodiment, sand or soil particles arecoated with a thin layer of hydrophobic common wax. In various aspects,a commercially available paraffin wax with the general formulaC_(n)H_(2n+2), where n>20 can be used to coat the surface of the sand orsoil. In other embodiments, sand particles can be coated with analternative to common wax. In any one or more aspects, the wax can havea boiling point of 65° C. or higher. Other hydrophobic alternatives tocommon wax can be paraffin wax, bees wax, soy wax, or palm wax. Forexample, sand or soil particles can be coated with paraffin wax soy wax,beeswax, candle wax and/or palm wax to functionalize the surface of thesand or soil to increase its hydrophobic or non-wetting properties orsurface co-efficient of friction.

On the other hand, processes as described herein can involve dilutesolutions of the wax, such as paraffin wax, in a solvent such asdichloromethane (an inexpensive solvent with a low dynamic viscosity(˜0.4 mPa-s) under ambient conditions. The resulting solutions have lowviscosity that are not stable within ±10° C. of the ambient conditions.Low viscosity implies lower energy cost during mixing. Lastly, thesolvent can be regenerated after a batch of sand or soil has been coatedwith ˜100 nm thick layer of wax for the next batch.

Methods as described herein can impart a surface modification ontoparticles of sand or soil by coating the particles with a substance,such as a hydrophobic substance, at a temperature, or over a range oftemperatures, and a pressure, or over a varying range of decreasingpressures. In an aspect, the temperature and pressure can be roomtemperature and standard pressure. Room temperature can be about 25° C.Room temperature can be about 20-25° C. Room temperature can be about20-28° C. Standard pressure can be about 1 atm or 1 bar.

In an aspect, the methods as described herein can be accelerated throughthe use of heat and/or altered or varying reduced, or negative,pressure. The temperature can be over a range of about 40° C. to about55° C. The pressure can be a negative pressure (meaning that the methodcan be operated under vacuum). The method can be started at a firstpressure (P1) during a first stage, then reduced during a second stageto a lower pressure (P2), and subsequently reduced again to yet a lowerpressure (P3) during a third stage. The pressure can be varied fromabout 1000 mbar during the first stage to about 10 mbar during the thirdstage to affect the superhydrophobic coating of the sand or soil.

The ratio of sand or soil to hydrophobic substance (also known as amodifying agent as used herein) can be about 1:200 to about 1:2000,about 1:300 to about 1:1000, about 1:400 to about 1:800, or preferablyabout 1:600 grams of modifying agent (e.g., wax) to grams of sand. Forsoils such as clay or silt with smaller particles sizes, the ratios canbe calculated based on total particle area to be coated.

The equation m_(wax)=τ·ρ_(wax)·m_(soil)·A_(BET) can be used to estimatethe mass of wax (m_(wax)) needed for a given soil mass (m_(soil)), withBET surface area of the soil (A_(BET)), density of wax (ρ_(wax)) anddesired thickness of coating (τ). Where the minimum thickness requiredcan be 10 nm, but higher values such as 20, 50 or 100 nm are preferredto guarantee a homogeneous coating, accounting for the uncertainties inthe measurements and surface chemistries. When the BET area is notavailable, its value can be estimated using A_(BET)=6/(d·ρ_(wax)·Ψ),where d is the average particle size of sand or soil, and W is theaverage sphericity of the particles.

Herein, an inexpensive solvent (such as mentioned above) can be employedto dissolve wax (with or without any external heat) and coat the surfaceof the sand or soil particles with a nanoscale thickness of the wax,i.e. less than 100 nm thick (as described above). Furthermore, thesolvent can be recovered and regenerated in the process to be used overand again.

A surface modification agent (or hydrophobic substance or modifyingagent) can be used in conjunction with a solvent to modify the surfaceof sand or soil particles. The surface modification agent can be ahydrophobic substance that can coat sand or soil particles. The surfacemodification agent can be a hydrophobic wax, such as common wax,paraffin wax, bees wax, soy wax, or palm wax. In an embodiment, thesurface modification agent is paraffin wax. In an embodiment of themethod, paraffin wax is used in conjunction with a solvent to coat sandor soil particles and impart hydrophobic properties to the particles.

With reference to FIG. 21, in an embodiment, the method of producingsuperhydrophobic sand or soil can comprise the steps of: a) obtaining asand or soil composition; b) washing the sand or soil composition; c)drying the sand or soil composition; d) obtaining a wax; e) dissolvingthe wax into a solvent to form a wax solution; e) adding the sand orsoil composition to a container; f) adding the wax solution to thecontainer; g) mixing the wax solution and the sand or soil compositionwithin the container at a first pressure (P1) and at a first temperaturefor a first period of time (t1); h) bringing the mixture up to but undera boil, or alternatively up to a boil over another time period (t3), forexample up to a slow boil; and i) subsequently maintaining the mixtureat a constant pressure for a final time period (t4) to form saidsuperhydrophobic sand or soil including the sand or soil compositioncoated with wax.

As illustrated in FIG. 22, in an embodiment, the method can furtherinclude the steps of: reducing the first pressure (P1) in the containerto a second pressure (P2) that is lower than the first pressure (P1)over a second time period (t2), the second time period (t2) being lessthan that of the first time period (t1); reducing the second pressure(P2) in the container at a constant rate over the third period of time(t3) to a third pressure (P3), the third period of time (t3) beinglonger than the second period of time (t2) and the third pressure (P3)being lower than the second pressure (P2); once reaching the thirdpressure (P3) maintaining the pressure in the container at the thirdpressure (P3) for the fourth and final period of time (t4); andnormalizing the pressure in the container from the third pressure (P3)up to atmospheric pressure to form said superhydrophobic sand or soilincluding the sand or soil composition coated with wax.

The solvent can be allowed to evaporate. The evaporated solvent can becondensed with a condensation system combined with a collection and/orstorage system and recycled for later use. Evaporation of the solventcan leave a thin layer of the surface modification agent, such as ahydrophobic wax on the sand or soil, producing a hydrophobic sand orsoil that can repel water. The thin layer can be 100 nm or less, asdescribed herein. The recovery of the solvent can be reduced in time byapplying heat and an amount of vacuum.

In various aspects, described herein is a method to reduce or preventwater evaporation in agricultural systems. Agricultural systems asdescribed herein can have soil, an irrigation source, a light source,and optionally fertilizer. Agricultural systems as described herein canbe irradiated and have a source of light, such as the sun or from bulbsin a lamp. Agricultural systems as described herein may be exposed tothe environment (i.e. outdoors) or may be shielded from the elements(i.e. indoor, such as in a greenhouse or within another structure).Agricultural systems as described herein may be within a structure thatis elevated from the ground. In an embodiment, an agricultural system isa field (that can have soil) with an irrigation source that isirradiated by the sun, as one would find on a farm, and can optionallyhave fertilizer. In one or more aspects, the method can includedistributing a layer of the aforementioned superhydrophobic sand or soilmulch over agricultural topsoil.

The present functionalized sand or functionalized soils, in particularthe present hydrophobic sand, such as sand as described above, can beused in agricultural systems to reduce water loss by evaporation. Thehydrophobic sand or soil can be used as a mulch. It can, for example, beused in agricultural systems and placed on top of topsoil to reduceevaporation. The hydrophobic sand or soil can be used in agriculturalsystems to reduce or prevent penetration of water beyond the hydrophobiclayer when placed underneath (or more subterranean) layers of top soilor other layers of soil or ground. The hydrophobic sand or soil can beused in agricultural systems to direct water via gravity towards plantedseeds, roots, or other plant constituents that are planted in or abovethe ground.

The hydrophobic sand or soil can be used in agricultural systems toreduce or prevent the deposition of common salts (such as NaCl) due tosalty (or desalinated or partially desalinated water) in topsoil. Thehydrophobic sand or soil can be used like a mulch, or in place of amulch, and can be used in agricultural systems to reduce or preventdeposition of minerals, metals, metalloids, heavy metals, alloys,elements, bacteria, fungi, or other constituents of impure water on topsoil. The hydrophobic sand or soil can be used to prevent passage ofsalts. In other aspects, the functionalized sand or soil describedherein can have an increased coefficient of friction to reduce it frombeing blown away in high winds such as during a desert sand storm.

Examples

Now having described various embodiments of the disclosure, in general,the examples describe some additional embodiments. While embodiments ofthe present disclosure are described in connection with the examples andthe corresponding text and figures, there is no intent to limitembodiments of the disclosure to these descriptions. On the contrary,the intent is to cover all alternatives, modifications, and equivalentsincluded within the spirit and scope of embodiments of the presentdisclosure

An inexpensive surface modification method of common sand or soil, forexample sand found in deserts, beaches, or arid regions, using commonwax, e.g. paraffin, bees, soy or palm wax, to render the sandhydrophobic was demonstrated (FIG. 1A). The hydrophobic sand or soil canbe used to reduce water consumption in desert or arid land agriculture.Demonstrated herein are compositions and methods that address both theaforementioned challenges of excessive water consumption and depositionof common salts elegantly and with minimal expense. The material andmethods can be placed (1) above (i.e., on top of) the soil to preventwater evaporation, and (2) under the soil at a depth, d, comparable totwice of the root depth, d_(r), to present a barrier to water frompenetrating deeper.

Example 1

The technology disclosed herein entails an inexpensive surfacemodification method of common sand or common soils with low organicmatter content, for example found in deserts, beaches, or arid regions,using common wax, e.g. paraffin, bees, soy or palm wax, to render itsuperhydrophobic. A variety of applications are proposed herein for thesuperhydrophobic material including desert agriculture, home gardening,liquid marbles, water proofing, corrosion-prevention, thermalinsulation, water desalination and reducing intensity of sand storms.Since the present superhydrophobic sand or soil is robust, non-toxic,inexpensive, and effectively repels water, it should fulfill all otherapplications claimed for similar granular media, comprising of sand orsoil and wax^(1-4, 6). (FIGS. 1A and 1B)

Sand or soil is intrinsically a hydrophilic porous medium due to polarSi—O—H bond and chemistries that ensue when water is placed on it.¹³ Forinstance, sand in the Saudi Arabian peninsula is a complex granularmixture of minerals, including mainly quartz (SiO₂), aragonite (CaCO₃),alumina (Al₂O₃), iron oxide (Fe₂O₃) and titania (TiO₂) with particlesizes, 75 μm<l<750 μm.¹⁴ To get a fair idea of the wettability of sandby water, we measured advancing and receding contact angles of water onsmooth and flat silica, the major constituent of sand, in air, and foundthem to be, θ_(Adv)=θ_(Rec)≈35°. Now, we try to understand what happenswhen a drop of water lands on ordinary sand—we expect that themechanical equilibrium between interfacial tensions would lead to aconcave meniscus, which satisfy the equilibrium contact angle,θ₀≈θ_(Adv)=θ_(Rec)≈35° (FIG. 2). This curvature creates a capillarypressure, known as the Laplace pressure that drives water into thegranular sand matrix. A magnitude of the Laplace pressure can beestimated by considering sieved sand particles to be approximatelyspherical with diameters 75 μm<d<150 μm and with spacing as shown inFIG. 2, which yields, P_(L)=2γ_(LV)×cos θ₀/r₂≈6-600 kPa, where γ_(LV)=73mN/m is the surface tension of the air-water interface, θ₀≈35° is theintrinsic/equilibrium contact angle at the wax-water-vapor interface,and r₂=200 nm-20 μm is an expected range for the radii of curvature dueto multiscale roughness of grains as shown in FIG. 2. In short, thismodel calculation explains why ordinary sand readily imbibes water.

It can be hypothesized that if sand or soil could be renderedhydrophobic (i.e. θ₀>90°), the curvature of the water meniscus at thesolid-vapor interface will be opposite to curvature of water in contactwith ordinary sand or soil (compare FIGS. 2 and 3A). Typically, smoothhydrocarbon surfaces have an intrinsic contact angle for the air-waterinterface, θ₀≈105°. Thus, following the abovementioned logic andapproximates, we estimate the magnitude of the Laplace pressure as,P_(L)=2γ_(LV)×cos θ₀/r₂≈1.9-190 kPa, which will prevent inhibition ofwater inward.

Methods for Coating the Sand or Soil:

In an embodiment, to render common sand or soil superhydrophobic, thefollowing protocol can be applied:

1. Sand from KAUST beach was tested and soil from the Makkah region inSaudi Arabia were tested. Other sands or soils, such as those describedabove, can be used;

2. The sand or soil was washed with water to remove organics, solublesolids and surfactants;

3. The sand or soil was dried in a thermal convection oven at 100° C.for 6 to 24 h. This step can also be done using sunlight and naturalwind convection to reduce the costs in an industrial application;

4. Mechanical sieving was used to isolate sand or soil grains with size<600 μm; This step is not required, but the sand or soil with smallergrain size, results in better hydrophobicity;

5. Blocks of paraffin wax are grated to sizes of the order of <1 mm tomake wax shavings;

6. The wax shavings are dissolved into an organic solvent (diethylether, pentane, dichloromethane, methyl-t-butyl ether (MTBE), petroleumether (ligroine), chloroform, tetrahydrofuran (THF), hexane,cyclohexane, triethyl amine, gasoline or toluene) in order to make a waxsolution. The solvent to sand or soil ratio can be in the order of 1 mLof solvent to 2 g of sand or soil;

7. The sieved sand or soil is then added to an appropriate container,for example a rotary evaporator; preferably this container is able tosupport vacuum and a pressure to about 10 mbar. It can also contain oneor more baffles in order to provide homogenous mixing of the waxsolution and sand or soil during evaporation;

8. The wax solution is then added to the same container. The wax to sandor soil ratio can be from 1:200 to 1:2000 grams of wax to grams of sandor soil, depending on the thickness of the coating required. For commonsoils with smaller particles sizes and greater particle area per mass,1:200 grams of wax per grams of soil or higher concentrations of wax canbe used;

9. Next, the wax solution and the sand or soil are mixed in thecontainer, for example by agitation (10 to 150 rpm, depending on therotary evaporator characteristics); the bath of the container, forexample the rotary evaporator, is maintained at 40° to 55° C. (T1). Thisprocess is under 1000 mbar of pressure (P1) and it takes 1 to 5 minutes(t1) in order to homogenize the wax solution with the sand or soil andto stabilize the temperature (See Table 1).

10. Then, depending on the solvent, the pressure is dropped to P2. Thisstep can be done rather quickly over a time (t2).

11. Once the system is at P2, the rate of pressure drop is decreased ata constant rate, as can be seen in Table 1 over a time (t3), until itreaches the final pressure P3.

12. Once at P3, the system is maintained at the pressure P3 for acertain time (t4) and then the pressure is normalized to atmosphericpressure and the batch is finished.

This treatment leaves a thin coating of wax on the surface of eachgranule of sand or soil, rendering hydrophobic properties in the sand orsoil to a ratio as low as 1 g of wax per 2000 g of sand or 1 g of waxper 200 grams of soil. However, it is preferred to use 1:600 grams ofwax to grams of sand, which leads to t 20 nm thick films on the sandparticles (FIG. 3B) or 1 g of wax to 50 grams of soil. Obviously, thethickness of wax coating can be tuned by increasing the wax to sand orsoil ratio.

TABLE 1 Settings for evaporation of different solvents t3 - t1 - t2 -P2 - Time Time Time Pressure from P3 - t4 - at P1 from P1 to P2 to FinalTime Molecular and to P2 boil P3 pressure at P3 Solvent Formula weightT1 (min.) (mbar) (min.) (mbar) (min.) diethyl ether C₄H₁₀O 74.12 1-5 01000 5-15 1000 1 pentane C₅H₁₂ 72.15 1-5 0 1000 5-15 1000 1dichloromethane CH₂Cl₂ 84.93 1-5 0 1000 5-15 1000 1 methyl C₅H₁₂O 88.151-5 0.5 700 5-15 500 1 t-butyl ether (MTBE) Petroleum C₅₋₆H₁₂₋₁₄ 72-861-5 0.5 900 10-25  160 5 ether (ligroine) chloroform CHCl₃ 119.38 1-50.5 700 5-15 500 5 tetrahydrofuran C₄H₈O 72.106 1-5 1 500 5-15 300 5(THF) hexane C₆H₁₄ 86.18 1-5 1 360 5-15 160 5 cyclohexane C₆H₁₂ 84.161-5 1 320 5-15 120 5 triethyl amine C₆H₁₅N 101.19 1-5 1.5 250 5-15 50 5toluene C₇H₈ 92.14 1-5 2 120 5-20 20 5

Materials:

The solvents and paraffin wax (molecular mass, M₀≈487 Da, melting pointT=65° C.) were purchased from Sigma Aldrich and used as is. In additionto paraffin wax, we tested beeswax, palm wax, and soy wax to find thatall behaved similarly. Other researchers have investigatedhydrophobization of sand, such as coating with (i) wax at 70-90° C.⁶,(ii) polystyrene¹⁵, (iii) silanes⁷, and (iv) sprayable biodegradablepolymers¹⁶. However, none of these methods have become mainstream so fardue to cost of chemicals or chemical processing. As a result, foragricultural applications, polyethylene-based plastic mulches remain themost used mulches in the western world, despite their disposal-relatedecological challenges.¹⁷⁻¹⁸

Characterization:

The wetting behavior of water on the present sand or soil wascharacterized rigorously. Contact angles of water microdroplets weremeasured on individual sand grains both before and after wax coating inan environmental scanning electron microscope (SEM). Whereas the contactangles were θ₀≈30° for ordinary sand, they increased to θ₀≈90° afterhydrophobization. (FIGS. 4A-4C) When wetting of packed beds of thepresent sand or soil was measured with a contact angle cell for larger,millimeter scale, droplets of water, superhydrophobic behavior wasobserved: advancing and receding contact angles, θ_(Adv)≈θ_(Rec)≈150°(FIG. 4C) and as a consequence, if the solid surface was tilted waterdrops rolled off at θ_(roll-off)≈5°. The difference between contactangles observed in the environmental SEM and apparent contact anglesmeasured by a contact angle cell can be easily explained by theentrapment of air in the latter case, known as the Cassie-state.¹⁹ Ifwater drops (2 μL) were allowed to impinge on a packed bed of thesuperhydrophobic sand from a height of 2 cm it recoiled off the surface(due to preventive Laplace pressure explained above) to eventually landas a liquid marble decorated with sand particles (FIG. 1B).

Resistance of the superhydrophobic sands against penetration of water ina hydrophobized glass cylinder was also measured: a ˜2-cm column of300-μm-sieved superhydrophobic sand was placed over cotton and filled tothe maximum a 60-cm column of water with rhodamine dye to aidvisualization (FIG. 5). This experiment was observed for over a weekduring the course of which water did not penetrate.

Next, the ability of the present sand was tested to determine itshydrophobic properties when mixed with common (hydrophilic) sand (FIG.6). It was observed that it was possible to place a droplet of water onthe mixtures of superhydrophobic sand: common sand to ratios as low as1:9. It is worth mentioning that this does not imply that the sandmixture is able to hold column of water as the pure 100% hydrophobicsand would. But this result is interesting, especially when comparedwith results obtained from U.S. Pat. No. 7,160,379¹. Their method forcoating was based on melting waxes and mixing with sand. Their methoddoes not provide a uniform coating over the surface of the sand grainsas evident from their data classified as follows: “good” when theirhydrophobic sand prevents penetration of a droplet of water for at least60 minutes. This “good” result is comparable to the result obtainedherein when the present hydrophobic sand (10%) was mixed with normalsand (90%). This evidences that the present coating methodology is muchsuperior to theirs. They only consider the hydrophobicity to be“excellent” when the sand bed is able to hold a water droplet for longerthan 60 minutes, which is a very low standard for hydrophobicity. Theprocesses that utilize the melted wax to coat sand either require muchmore wax than the present method(s) or they produce bad quality coating,which is the case for the cited patent U.S. Pat. No. 7,160,379¹.

Notably, the present process for making sand or soil hydrophobic onlyuses 1 g of wax per 200 g of sand, preferably per 600 g of sand (goodresults were even obtained when 1 g of wax was used per 2000 g of sand).The process cited in U.S. Pat. No. 7,160,379¹ claims to use from 0.01 to10% (Weight ratio of Wax blend to total coated sand Weight), processesas described herein were able to effectively use 0.050% (1 g of wax per2000 g of sand) and truly make hydrophobic sand. Essentially, thepresent process uses much less wax for coating sands and is able to makea much more homogeneous coating, providing a more reliable process.

Example 2: Preventing Evaporation of Moisture from Pots

In order to measure the effectiveness of superhydrophobic sand or soilmulches on reducing evaporative losses in pots under ambient conditions,changes in the masses of pots containing soil (Metro Mix 360) coveredwith varying thicknesses of superhydrophobic sand were tracked over time(FIG. 7A). As shown in FIG. 7B, it was found that application ofsuperhydrophobic sand can suppress evaporation of water from thetop-soil significantly; in comparison, application of simple sandexhibited poor performance. From these data, 5 mm thick layers ofsuperhydrophobic sands were exploited in our following experiments.

To test the effectivenesss of reducing evaporative loss of water frompots, pot-scale experiments were conducted at the KAUST greenhouse.These experiments employed hydrophobic sand mulch as a top layer toreduce evaporation at the pot scale over a 7 weeks cycle for tomato andbarley plants (as illustrated in FIG. 8). These experiments producedoverwhelmingly positive results for tomato plants (Table 2 below). Dueto higher retention of water in the soil covered with hydrophobic sand,the mass of shoots were 92% higher and roots 63% than control sample.Similar experiments were conducted for barley and mixed results wereobserved (Table 3).

The differences were attributed to plant physiology.

TABLE 2 Tomato results for pot-scale experiment performed in KAUSTgreenhouse Mean water Breakdown of Total % water loss loss every (Total% water loss = Mean day (%): water loss everyday (%)) Productivity Massfraction of M_(Added daily) % loss via % loss via Mass of Mass of waterin soil M_(50%) × 100 evaporation transpiration shoots (g) roots(g)Normal irrigation 15.4 78.0 22.0 16.46 2.6 (Control) i. Normal 17.3 34.865.2 31.58 4.23 irrigation + (92% (63% superhydrophobic higher) higher)sand Drought condition 18.0 66.6 33.3 12.96 2.2 (Control) ii. Drought13.6 43.8 56.2 19.52 2.24 condition + (50%  (2% superhydrophobic higher)higher) sand

TABLE 3 Barley results for pot-scale experiment performed in KAUSTgreenhouse Mean water Breakdown of Total % water loss loss every (Total% water loss = Mean day (%): water loss everyday (%)) Productivity Massfraction of M_(Added daily) % loss via % loss via Mass of Mass of waterin soil M_(50%) × 100 evaporation transpiration shoots (g) roots (g)Normal irrigation 18.0 66.6 33.3 28.47 17.25 (Control) i. Normal 18.033.3 66.6 32.71 19.32 irrigation + (15% (12% superhydrophobic higher)higher) sand Drought condition 17.3 69.6 30.4 20.85 10.99 (Control) ii.Drought 11.0 54.5 45.5 15.32 10.21 condition + (26%  (7%superhydrophobic lower) lower) sand

Example 3: Preventing Evaporation from Soils in Irrigated Agriculture

Motivated by the experiments at the KAUST Greenhouse, field-scaleexperiments were conducted in western Saudi Arabia (Hada al sham,21.799° N, 39.725° E) to test the impact of the hydrophobic sand mulchon the performance of two locally relevant crop species in desertagriculture settings under low and high salinity irrigation. Tomato(Solanum lycopersicum cv. Nunhems Tristar F1), a low planting densityhigh-value horticultural dicot crop, and barley (Hordeum vulgare L. cv.Morex), a monocot crop grown at high densities typical for cereals, werechosen to gain insights into the applicability of superhydrophobic sandsin different agronomical contexts. Additionally, the potential benefitsof the hydrophobic sand or soils for crop performance under salinitystress were assessed, a prevalent source of abiotic stress in desertagriculture that often co-occurs with water deficit. As such, plots oftomato and barley grown with either (i) bare soil or a ˜5 mm layer ofhydrophobic sand, and (ii) low or high salinity irrigation, withendpoint phenotyping of various traits at harvest (example of set upshown in FIG. 9).

Twenty-four sensors were employed directly under the plants to measureconductivity, temperature, and moisture content. In the tomato field,superhydrophobic sand was applied in 3 strips per plot, being 40 cm thewidth of the mulch line and the length extended 20 cm from the externalplants in the plot lines (FIGS. 10A-10B). For the barley plots, the sandcovered the entire area of the plot and extended 20 cm from the outerplants of the plot. The thickness of the sand layer in all plots was ˜5mm. Three dripping lines were installed in each of the tomato plots,along with six in the barley plots. The area directly under drippers wasleft uncovered with the superhydrophobic sand in other to allow forwater infiltration. This system can be improved in future experiments,as the drippers can be buried to guarantee complete water infiltration.

The sensors measured volumetric water content (VWC), defined as theratio of the volume of water present in the soil to the volume of thesoil²⁰. As shown in FIGS. 11A-11B, it was found that VWC wassignificantly higher for both tomato and barley fields when a 5 mm thicklayer of superhydrophobic sand was applied on the top-soil in comparisonto bare top-soil (control case).

Mulched tomatoes exhibited significant improvements over unmulched inall traits under both low and high salinity irrigation (FIGS. 12A-12B).In contrast, under low salinity irrigation mulching in barley had alimited effect on most traits, with only grains FM increasingsignificantly in mulched barley plots. Interestingly, significantlyenhanced performance was recorded for all traits under salt stress inmulched barley relative to unmulched. In line with the expectations, thehydrophobic sand mulch tended to benefit crop performance, ostensibly byraising soil moisture levels. Furthermore, mulching overwhelminglyimproved performance under high salinity irrigation by attenuatingsalinity stress through the reduction of sodium concentrations in thesoil—a dilution effect caused by the additional water. This is largelyattributed to the disparities between the two crop species tocontrasting planting densities. The greater spacing between tomatoplants likely leads to higher levels of evaporation due to increasedexposure of the soil surface to the elements, and thus more pronouncedbenefits from the protective qualities of the hydrophobic sand mulchunder both low and high salinity irrigation. On the other hand, thetight canopy formed in high planting density barley plots may provide anadequate buffer to prevent excessive evaporation under controlconditions. It is likely that the mulch still increases soil moisture,as indicated by enhanced performance under salt stress, but that thisoccurs beyond the threshold that is limiting for plant growth. Overall,these results show the hydrophobic sand mulch or layer significantlyimproved crop performance by increasing soil moisture levels.Furthermore, the results indicate that the hydrophobic sand mulchbenefits particularly low planting density crops such as tomato. Thissuggests similar results could be obtained with other crops with similaragronomical practices, which tend to be high value horticulturalspecies, such as peppers and aubergines. Furthermore, these resultspoint towards effective applications of hydrophobic sand or soil mulchesin cereal crops, whose agronomical practices preclude the use ofconventional plastic mulches, for combatting salinity stress inparticular.

Example 4: Liquid Marbles Made with Superhydrophobic Sand

Against common expectation, granular hydrophobic media can encapsulatewater droplets and the resulting material is known as Liquid marbles(FIG. 13)²¹⁻²². Here, we report on the nature of liquid marbles obtainedby trapping water drops inside a monolayer of hydrophobic sand particlesby rolling a water droplet, on to a bed of sand (FIG. 13).

Interestingly, liquid marbles formed by capturing 10-μL dropletsdeionized water in our superhydrophobic sand demonstrated a 50% slowerrate of evaporation under ambient conditions (T=294 K, P=1 atm, 60%relative humidity) (FIG. 14 and FIG. 15).

Equation 1 shows the evaporation model used, where D is the diffusionconstant and k is the resistance for evaporation, set to 1 in the caseof droplets and it assumes a value higher than 1 for marbles.Evaporation rates were modeled as a function of radius (r), surfacearea, and volume of the droplets (FIG. 15).

$\begin{matrix}{\frac{dm}{dt} = {{- \frac{D}{k}} \cdot r \cdot \left( {P_{sat} - P} \right)}} & {{Eq}.1}\end{matrix}$

The ability to hold water for longer times than common water dropletscan unlock potential applications as microbial reactors. Water dropstrapped inside liquid marbles do not readily coalesce when pressedagainst each other. Thus, by capturing water in liquid marbles,advantage can be taken of large surface area to uptake gases at theliquid interface that microbes could metabolize.

Example 5: Superhydrophobic Sand or Soils for Reducing Dust Acumulation

The wax coating in our superhydrophobic sands increases the coefficientof friction (tangent of half, of 180 degrees minus the cone angle)(FIGS. 16A and 16B) between the grains, making it more difficult forwind to move the bigger particles and lift the smaller ones (FIGS. 17Aand 17B).

Thus, the present superhydrophobic sand or soil can be used to coverareas around solar farms or cities in desert lands in order to reducethe dust lifting from those areas and thus, reduce the dust accumulationon solar panels, houses, or other objects.

Example 6: Superhydrophobic Sand or Soil for Corrosion Prevention,Thermal Insulation and Easier Maintenance of UndergroundPipes/Cables/Electronic Devices/Other Objects

The present superhydrophobic sand or soil can also be used inconstruction to fill ditches/trenches/cavities that have cables,pipelines or other corrosion-prone objects buried. By using thesuperhydrophobic sand or soil instead of common soils or otherhydrophilic materials, moisture in the common soil would not infiltratetowards those objects. This insulation would reduce corrosion problem inmetallic objects, such as pipelines and electrical equipment. It wouldalso prevent soil compaction around those objects, facilitating futuremaintenance/excavation of the objects buried (cables or pipeline forinstance). The dry superhydrophobic sand or soil filling around thoseburied objects would also act as a cheap thermal insulator, thus,reducing the thermal losses or gains in fluid pipelines.

Example 7: Superhydrophobic Sand for Rooftop Thermal and HumidityInsulation

The superhydrophobic sand can be used to cover roofs of houses or othertypes of buildings. This sand layer would act as a thermal insulator.The big advantage here is that rain would not accumulate on the roofs,decreasing the possibility of mold growth or infiltration.

Example 8: Superhydrophobic Sand or Soil for Insulation of Foundationsof Buildings Against Soil Moisture

Superhydrophobic sand or soil can be used to insulate undergroundfoundation from humid soils, which would reduce water infiltration,growth of mold, percolation of salt, and provide thermal insulation

Example 9: Superhydrophobic Sand or Soil for Waterproof Pavement Bases

The superhydrophobic sand or soil can be used as a waterproof base layerfor the construction of pavements that suffer from soil moisture uptake.Changes in the moisture content make soils expand or contractaccordingly, causing structural problem with pavements. By applying alayer of hydrophobic sand or soil between the humid soil and thepavement, the impact of soil activity can be reduced.

Example 10: Superhydrophobic Sand or Soil for Making Freeze-Proof Soils

Since water expands during freezing, changing from liquid to solidstate, formation of ice could cause severe structural damages to walls,pipes, or other objects. By preventing infiltration of water,superhydrophobic sand or soil would prevent formation of ice in ground.Thus, the present superhydrophobic sand or soil can also be used as afreezing-proof insulating layer around a variety of objects.

Example 11: Superhydrophobic Sand or Soil for Preventing WaterPercolation

Superhydrophobic sand or soil can be used as an underground layer(several centimeters thick) to prevent water percolation in agriculturalland (to reduce the needs of irrigation), sewage canals or landfillareas (to prevent percolation of contaminated waters down to theunderground water table), irrigation canals (to prevent water lossthrough percolation), or even as a safety barrier to preventinfiltration of contaminated liquids (the sand or soil can be tested foreach liquid) spread as a thick layer on the ground around tanks(containing hazardous liquids) with risk of leakage.

Example 12: Superhydrophobic Sand or Soil for Membrane Distillation

Membrane distillation is a method to desalinate water wherein twostreams of water are separated across a superhydrophobic membrane. Asillustrated in FIG. 3A, liquid water cannot pass through this membrane.Typically, a hot feed solution (e.g. seawater at 70° C.) is on one sideof the membrane and a cold stream (e.g. 20° C.) on the other. Due totheir superhydrophobicity, the material can be suitable for thisapplication.

Membrane Distillation (MD) is a promising low-energy techniquecommercially employed that can be used for applications such as waterdesalination or removal of other impurities. It can use waste heat, e.g.from industry, to heat up the feed water (which can be salty) to ˜50-70°C., and a hydrophobic membrane with small pore sizes that only allowwater vapor to pass through. Water vapor can then be condensed on theother side (FIGS. 18A and 18B)).

The use of wax-coated sand or soil as described herein as thesuperhydrophobic membrane is shown in FIG. 18A. Use of wax-coated sandor soil as a membrane involves placing the hydrophobic sand or soil in aflexible net or container (with pore size smaller that sand or soil) tosecure it. The superhydrophobicity of wax-coated sand or soil and thesmall sizes of coated sand grains or soil particle scan generate highLaplace pressure (explained in FIGS. 2 and 3A above) which can preventliquid water from the feed from traveling to the permeate side or viceversa. One skilled in the art would recognize in membrane distillationthe membrane must withstand the pressure applied on the feed waterside.Thus, the higher the Laplace pressure, the higher will be its tolerance.Thus, only water vapor will pass through (FIG. 18B). An advantage ofusing hydrophobic sand or soil is that it can be inexpensive compared toother methods. Further, it may provide flexibility to choose pore sizesto tune flux. Milling coated sand or soil and ball-milled to finer(nanoscale) sizes is an example of how particles may be tuned to alterflux.

A membrane distillation process as described herein typically applies apressure (2-4 bar) and temperature (50-90° C.) on the feed water (i.e.salty water) side of the membrane. Thus, while liquid water cannot passthrough a cartridge/membrane made of wax-coated sand or soil due tocapillarity, water vapor can due to the pressure and/or temperaturedifference across the membrane. Further, this process utilizes thinmembranes to minimize losses in the transport of vapor flux. (On theother hand, to reduce evaporation in agriculture, thicker wax-coatedsand or soil layers can be more effective.)

Example 13: Inhibition of Evaporative Water Loss from Ordinary Soil whenCovered by a Hydrophobic Sand Layer Under Desert-Like Conditions

To quantify the effect of a top-layer of hydrophobic sand or soil onreducing evaporative loss of water throught ordinary agriculture soil (3cm thick), pot-scale experiments were conducted employing standard massbalance (accuracy 0.01 μm) over a period of 2 days (Average temperature:24.7° C., Relative Humidity: 70.5%). A 2-3 mm thick layer of hydrophobicsand on ordinary soil was observed to reduce evaporative loss of waterby 48% over a 24 hour period (FIG. 19). This result shows that employinghydrophobic sand as a cover for agricultural soil can dramaticallyreduce water losses via evaporation. In turn, this can result in asignificant reduction in the consumption of irrigation water andautomatically reduce the perils of sodication (i.e. deposition of highconcentrations of salts) in the top soil over time due to irrigationwith partially salty water, as is the case in arid regions near largesources of salt water.

Field scale testing of hydrophobic sand towards reducing irrigationneeds is a consideration for validating potential uses of hydrophobicsand or soil. For example, parts of fields can be covered withhydrophobic sands or soils to facilitate focused irrigation (FIG. 20)near seeds during tilling (because water will not wet hydrophobic areasand will be driven to hydrophilic soil right above the seeds). Anotherkey advantage from covering agricultural soils with hydrophobic sand orsoil is that the farm soil can retain higher water content than withouthydrophobic sand or soil. This can ensure that crops/plants undergolower water stress on a regular basis (daily), and can lead to improvedcrop yields. Further effects of degradation of wax by soil-bornebacteria and any unexpected deleterious effects of hydrophobic sand orsoils, such as leaching of residual solvents, can also be tested toensure long-term safety relating to the use of hydrophobic sand or soilsin agriculture.

The superhydrophobic behavior of the functionalized sand or soil asdescribed herein repels liquid water (FIGS. 1A and 1B). One skilled inthe art would recognize that in the presence of the functionalized sandor soil, such as a wax-coated sand or soil layer, liquid water insidethe soil cannot climb up all the way up to the soil-air interface, viacapillarity, and evaporate directly due to solar radiation for exampledepicted as in FIG. 3(a) and as compared to FIG. 2. Instead, thetemperature of the whole soil surface has to rise significantly toevaporate water in the soil before it can escape via molecular diffusion(which depends on ambient, temperature and relative humidity). Hence, adecrease in loss of moisture content in soil is seen when a layer ofwax-coated sand is placed on top (FIG. 20). This decrease will be higherfor thicker functionalized, for example wax-coated, sand layers.

Example 14: Market and Cost Analysis

Already, there are some teams/companies selling hydrophobic sands fordesert agriculture, but their acceptance has been limited due to costand ease of usage. For example, Desalt Innovation Middle East (DIME),UAE, is selling product which if used in 5-10 cm thick layers canprovide a hydrophobic barrier using a proprietary German technology thatwe suspect the process to involve functionalization via organosilanes.⁷Note that 5 mm thick layers will necessitate 67,000 kg of hydrophobicsand (giving the mass density of 1.5 g/cc) to cover 1 hectare (10,000m²). There are other reports 90 g of wax was employed to modify 1 kg ofsand.

A strategy can be to employ the cheapest raw materials along withstraightforward processing and reuse of reagents. Thus, paraffin wax, aby-product of the petroleum industry, can be chosen as the additive anddeveloped a process to recycle the solvent employed to dissolve it.Presented below is a model calculation for cost estimation.

1 kg of paraffin wax can be employed for 600 kg of beach sand, forexample, and a suitable organic solvent to dissolve wax. Thus, the costof hydrophobic sand can be simply offset by a month of water usage. Itcan then be estimated that the cost of manufacturing the presentsuperhydrophobic sand, including materials (sand, wax, solvent), and theenergy requirements would be around USD $8/ton in 2017, and by addingthe costs for spreading a 5 mm layer on agricultural land, the cost canbe estimated to be around USD $8/ton or USD $620 per full hectare in2017. Also, taking into account that usually, the area covered by thesand mulch is only around 2 cm to each side of the plants, this wouldreduce the area in which the mulch would be applied to about 40% of thetotal agricultural land. Thus, the cost of the hydrophobic sand mulch isreduced to USD $250 per hectare in 2017.

Considering that high-value crops can grown in deserts, such astomatoes, flowers (perennials), strawberries, and dates will definitelybenefit from this innovation because they can yield higher profits for agiven agricultural area, easily offsetting the costs of the hydrophobicsand mulch. It is expected that the wax coating layer to last for atleast one year in field conditions. In comparison, the DIME HydrophobicMaterials gives a 30 years guarantee. A key advantage of our wax coatingis that it is biodegradable²³ and it will not keep the sand or soilhydrophobic for longer than the period for total wax degradation. Fieldtests demonstrated that the present superhydrophobic sand or soilmaintained its wetting behavior in harsh climate for at least 6 months.The pot-scale experiments have confirmed ability to last over a year.

An exemplary life cycle of the hydrophobic sand or soil mulch caninclude: (1) start with common sand or soil and wax, (2) manufacture thehydrophobic sand or soil with the methodology described herein, (3)place a layer of hydrophobic sand on topsoil to use as a barrier forwater evaporation (mulch), (4) grow higher quality crops with lesserwater and fertilizers, reapply the hydrophobic sand or soil mulch in theareas that are damaged due to soil tilting after each crop cycle or oncethe hydrophobic coating has been degraded.

Due to their inert nature, compositions of hydrophobic sand or soil asdescribed herein can last for years, further supporting the inexpensivenature of these compositions and methods as replacement of sand may notbe frequently needed. Yet, over time, the material is biodegradable andwill not contaminate the soil.

Example 15: Prevention of Storms in Deserts

Dust storms are formed when winds can ‘lift’ small particles of dust(sand) into the atmosphere. They cause various large-scale challenges inthe MENA region, for example, respiratory illness, poor visibility forroad- and air-traffic, dust accumulation and subsequent abrasion inmachinery, and dust accumulation on solar panels leading to lowerefficiency. Wax-coated sand or soil can be a cost-effective technologyto prevent the formation of dust or sand storms, if specific locationswhere regional winds lift maximum amount of dust or sand are known;identifying locations particularly susceptible to large amounts of dustbeing lifted by regional winds can be done via satellite imaging, forexample. Coating sand or soil particles with a hydrophobic substancealters surface properties of the sand or soil. Increasing thecoefficient of friction between wax-coated sand particles is an exampleof such. Altered surface properties, such as a higher coefficient offriction, can reduce/arrest their movements under a shear flow of fluid,such as a flow of air or a flow of water. Effects of raising thecoefficient of friction between particles of sand by coating with ahydrophobic substance, such as wax, can be seen as validated by theexperiments described below.

Coefficient of friction: In two separate experiments, approximately 90grams of ordinary and wax-coated sand were dropped via a 2 mm wide glassorifice on a flat and smooth stainless steel surface from a height of 5cm. The resulting shapes of the pyramids composed of sand grains werecompared (FIGS. 16A and 16B). It was found that the angle at the topvertex of the pyramid decreased from ordinary (102.83°) to wax-coatedsand (81.57°). This simple experiment demonstrates that the wax-coatedsand can have a higher average coefficient of friction than theordinary, non-coated, sand.

Sand transfer in simulated wind: A simple device such as a blow dryercan be used to simulate a shear flow of air or wind. A blow dryer can beturned on and applied to a mass of sands, non-coated and coated, andmass transfers following exposure to a shear flow of air can be comparedfor the two sand samples. Approximately 80 g of non-coated, “normal”,sand was put on a petri dish, and 80 g of coated sand was put on asecond petri dish, and the two samples were exposed to lateral airflow.A schematic is shown in (FIG. 17A). Sand samples can be exposed tolateral air flow as-is, or after baking at 50° C. for 24 hours (tosimulate the heat of the sun). It was found that the mass transfer forthe case of wax-coated sand, as-is and after baking at 50° C. for 24hours, was dramatically lower, as shown in FIG. 17B. Since the waxcoating is at the nanoscale, the effect can be due to the enhanceddensity of wax-coated sand, but due to its higher coefficient offriction, as demonstrated above. Further, wax-coated sand can also beexpected to form a percolation network under the intense heat of thesun, which might further decrease the mass transfer.

Example 16: Superhydrophobic Sand or Soil Mulches to Reduce EvaporativeLosses and Enhance Productivity in Desert

See Attachment A, the entire contents of which are incorporated hereinby reference.

Example 17: Controlling Evaporation Rates of Water Droplets Trapped asLiquid Marbles in Superhydrophobic Sands or Soils

See Attachment B, the entire contents of which are incorporated hereinby reference.

Ratios, concentrations, amounts, and other numerical data may beexpressed in a range format. It is to be understood that such a rangeformat is used for convenience and brevity, and should be interpreted ina flexible manner to include not only the numerical values explicitlyrecited as the limits of the range, but also to include all theindividual numerical values or sub-ranges encompassed within that rangeas if each numerical value and sub-range is explicitly recited. Toillustrate, a concentration range of “about 0.1% to about 5%” should beinterpreted to include not only the explicitly recited concentration ofabout 0.1% to about 5%, but also include individual concentrations(e.g., 1%, 2%, 3%, and 4%) and the sub-ranges (e.g., 0.5%, 1.1%, 2.2%,3.3%, and 4.4%) within the indicated range. In an embodiment, the term“about” can include traditional rounding according to significant figureof the numerical value. In addition, the phrase “about ‘x’ to ‘y’”includes “about ‘x’ to about ‘y’”.

It should be emphasized that the above-described embodiments are merelyexamples of possible implementations. Many variations and modificationsmay be made to the above-described embodiments without departing fromthe principles of the present disclosure. All such modifications andvariations are intended to be included herein within the scope of thisdisclosure and protected by the following claims.

REFERENCES

-   1. Shoshany, H.; Shoshani, A., Hydrophobic sand treated with wax    blend. Google Patents: 2007.-   2. Method for preparing hydrophobic sand by taking paraffin and    waste polyethylene plastic as raw materials. Google Patents: 2015.-   3. Thermal insulation water-proof sand and producing technique    thereof. Google Patents: 2003.-   4. Beermann, N., Rigid sand body, method for producing the same, use    thereof and method for producing grains of sand coated in wax.    Google Patents: 2001.-   5. Ogawa, K.; Hirasawa, Y.; Oshima, T.; Nishimura, Y., Artificial    soil structure and a method of preventing land desertification using    the same. Google Patents: 1996.-   6. Hydrophobic sand preparation method adopting wax and sand as raw    materials. Google Patents: 2013.-   7. Salem, M. A.; AI-Zayadneh, W.; Cheruth, A. J., Water Conservation    and Management with Hydrophobic Encapsulation of Sand. Water    Resources Management 2010, 24 (10), 2237-2246.-   8. Compound construction waterproof powder and its production    method. Google Patents: 1993.-   9. Heat-insulating hydrophobic powder and production thereof. Google    Patents: 1992.-   10. Granular water-proof heat-insulation building material. Google    Patents: 1999.-   11. Lamoreaux, M. A., Soil mixture and method of making same. Google    Patents: 1990.-   12.    A toluene solution of paraffin and sand as raw material preparation    method of the hydrophobic sand. Google Patents: 2015.-   13. de Gennes, P.-G., Brodchard-Wyart, F., Quere, D., Capillarity    and Wetting Phenomena. Drops, Bubbles, Pearls, Waves. Springer; 2004    edition: 2003.-   14. Prakash, P. J.; Stenchikov, G.; Kalenderski, S.; Osipov, S.;    Bangalath, H., The impact of dust storms on the Arabian Peninsula    and the Red Sea. Atmospheric Chemistry and Physics 2015, 15 (1),    199-222.-   15. Hydrophobic sand preparation method adopting waste polystyrene    foam as raw material. Google Patents: 2013.-   16. Adhikari, R.; Bristow, K. L.; Casey, P. S.; Freischmidt, G.;    Hornbuckle, J. W., Novel sprayable biodegradable polymer membrane to    minimise soil evaporation. 2015 International Conference on    Technology for Sustainable Development (Ictsd-2015) 2015.-   17. Kasirajan, S.; Ngouajio, M., Polyethylene and biodegradable    mulches for agricultural applications: a review. Agronomy for    Sustainable Development 2012, 32 (2), 501-529.-   18. Hillel, D., Introduction to Soil Physics. Academic Press: 1982.-   19. Kaufman, Y.; Chen, S. Y.; Mishra, H.; Schrader, A. M.; Lee, D.    W.; Das, S.; Donaldson, S. H.; Israelachvili, J. N., Simple-to-Apply    Wetting Model to Predict Thermodynamically Stable and Metastable    Contact Angles on Textured/Rough/Patterned Surfaces. Journal of    Physical Chemistry C 2017, 121 (10), 5642-5656.-   20. Bilskie, J., Soil water status: content and potential. Campbell    Scientific, Inc. 2001.-   21. McHale, G.; Newton, M., Liquid marbles: topical context within    soft matter and recent progress. Soft Matter 2015, 11 (13),    2530-2546.-   22. Janardan, N.; Panchagnula, M. V.; Bormashenko, E., Liquid    marbles: Physics and applications. Sadhana 2015, 40 (3), 653-671.-   23. Atlas, R. M., Microbial-Degradation of Petroleum-Hydrocarbons—an    Environmental Perspective. Microbiological Reviews 1981, 45 (1),    180-209.

The invention claimed is:
 1. A modified composition of sand or soil thatacts as mulch, comprising: one or more particles of sand or soil,wherein the one or more particles have a size which is 600 μm or less;and a hydrophobic layer coating each of the one or more particles ofsand or soil, wherein the hydrophobic layer includes a hydrophobicsubstance, and a ratio of (1) an entirety of the hydrophobic substancemaking up the hydrophobic layer and (2) the one or more particles ofsand or soil is between 1:300 to 1:1000 by weight so that water does notpenetrate through the modified composition of sand or soil after oneweek.
 2. The composition of claim 1, wherein the hydrophobic layer andone or more particles of sand or soil have a liquid roll off angle ofabout 3 to 7 degrees.
 3. The composition of claim 1, wherein the one ormore particles of sand or soil comprises SiO₂, CaCO₃, Al₂O₃, Fe₂O₃,TiO₂, P₂O₅, K₂O, CaO, MgO, Na₂O or MnO₂.
 4. The composition of claim 1,wherein the one or more particles of sand are beach sand or desert sandand one or more particles of soil are silt or clay soils.
 5. Thecomposition of claim 1, wherein the hydrophobic substance includes onlya single hydrophobic material.
 6. The composition of claim 1, whereinthe hydrophobic layer is wax, and the wax is selected from the groupconsisting of common wax, paraffin wax, palm wax, bees wax, and soy wax,individually or in combination.
 7. The composition of claim 1, whereinthe hydrophobic layer has a thickness of 20 nm.
 8. A method of reducingirrigation requirements for an agricultural system, comprising:providing a mulch that includes one or more particles of sand ormodified soil, wherein the one or more particles have a size which is600 μm or less, and each of the one or more particles is coated with ahydrophobic layer having a hydrophobic substance, and a ratio of (1) anentirety of the hydrophobic substance making up the hydrophobic layerand (2) the one or more particles of sand or soil is between 1:300 to1:1000 by weight so that water does not penetrate through the modifiedcomposition of sand or soil after one week; and distributing the mulchon one or more apexes of a soil for preventing water evaporation fromthe soil.
 9. The method of claim 8, further comprising: distributing themulch on a homogenous layer of 1 mm to 10 cm on top of the soil; andirrigating the soil.
 10. A modified composition of sand or soil thatacts as mulch, comprising: one or more particles of sand or soil,wherein the one or more particles have a size which is 600 pm or less;and a hydrophobic layer individually coating each of the one or moreparticles of sand or soil, wherein the hydrophobic layer around each ofthe one or more particles of sand or soil includes a hydrophobicsubstance, and a ratio of (1) an entirety of the hydrophobic substancemaking up the hydrophobic layer and (2) the one or more particles ofsand or soil is between 1:300 to 1:1000 by weight so that water does notpenetrate through the modified composition of sand or soil after oneweek.
 11. The composition of claim 10, wherein the hydrophobic layer andthe one or more particles of sand or soil have a liquid roll off angleof about 3 to 7 degrees.
 12. The composition of claim 10, wherein theone or more particles of sand or soil comprises SiO₂, CaCO₃, Al₂O₃,Fe₂O₃, TiO₂, P₂O₅, K₂O, CaO, MgO, Na₂O or MnO₂.
 13. The composition ofclaim 10, wherein the one or more particles of sand are beach sand ordesert sand and one or more particles of soil are silt or clay soils.14. The composition of claim 10, wherein the hydrophobic substanceincludes only a single hydrophobic material.
 15. The composition ofclaim 10, wherein the hydrophobic layer is wax, and the wax is selectedfrom the group consisting of common wax, paraffin wax, palm wax, beeswax, and soy wax, individually or in combination.
 16. The composition ofclaim 10, wherein the hydrophobic layer has a thickness of 20 nm.